The present invention fundamentally has the goal of depositing materials with reactive plasma-enhancement i.e. by a PE-CVD method, on a deposition surface, on the one hand with maximally high deposition rate onto the deposition surface, on the other hand, at minimally low temperature of this surface.
We define the deposition rate as the material thickness applied onto a surface per unit time, if said surface is disposed within the vacuum container at a defined site yet to be explained, since, in particular in the present context, the quantity of material deposited onto a surface unit per unit time is a function of the location at which the surface is disposed.
It is known from xe2x80x9cPlasma-Enhanced Chemical Vapour Deposition of Epitaxial Silicon from Silanxe2x80x9d, S. R. Shanfield et al., 1046 B, Extended Abstracts, Vol. 83-1 (1983), May, Pennington, N.J., USA; XP-002056339, to deposit epitaxial silicon layers by means of PE-CVD, with silane as the reactive gas. Therein a substrate temperature between 700xc2x0 and 900xc2x0 results. Coating rates (FIG. 3) of maximally 40 nm/min are achieved.
From xe2x80x9cLow Temperature Deposition of Microcrystalline Silicon in a Multipolar Plasmaxe2x80x9d, T. D. Maintei et al., 1046 B Extended Abstracts, (1985), October, No. 2, Pennington, N.J., USA; XP-002056340, is further known to deposit microcrystalline silicon layers with a PE-CVD method at coating rates up to approximately 40 nm/min at a surface temperature of 100xc2x0 C. and up to approximately 25 nm/min at a surface temperature of 250xc2x0 C.
From DE-OS 36 14 384 by the same applicant as the present application it is known to attain by means of a PE-CVD method using a low-voltage high-current arc discharge coating rates of 200 nm/min in the coating with nickel in Ni(CO)4 gas as the highest deposition rate specified there. Si is therein only deposited at a coating rate of approximately 17 nm/min. With the aid of the low-voltage discharge a homogeneous dense plasma is generated in the vacuum container.
According to xe2x80x9cPlasma-Assisted CVD of Diamond Films by Hollow Cathode Arc Dischargexe2x80x9d, J. Stiegler et al., Diamond and Related Materials, 2 (1993), 413-416, it is known to deposit diamond layers with a PE-CVD method at a deposition rate of up to approximately 35 nm/min at surface temperatures of at least 700xc2x0 C.
Furthermore known from xe2x80x9cLow Temperature Plasma-Enhanced Epitaxy of GaAsxe2x80x9d, K. P. Pande, 1046 Journal of the Electrochemical Society, 131 (1984), June, No. 6, Manchester, N.H., USA, is to deposit GaAs epitaxial layers at low temperatures below 400xc2x0 C., however, at deposition rates of 80 nm/min, however only starting at temperatures about 500xc2x0 C.
U.S. Pat. No. 5,554,222 discloses depositing diamond-like layers at relatively cold deposition surface temperatures of 250xc2x0 C. when cooled, and 400xc2x0 C. when not cooled. Deposition rates of 20 nm/sec were reported.
From PCT/CH98/00221 by the applicant of the present application it is further known to attain by means PE-CVD deposition rates of approximately between 100 and 200 nm/min, depending on the deposition materials, at surface temperatures between 300xc2x0 and 800xc2x0 C.
It is the task of the present invention to propose a method for the reactive plasma-enhanced deposition of material onto a deposition surface, by means of which at low temperatures of the deposition surface, without it being cooled, significantly higher deposition rates are attained compared to such prior known PE-CVD methods.
This is achieved through the use of a method for the reactive plasma-enhanced treatment of workpieces, in which a plasma beam is generated in an evacuated container and workpieces are disposed radially offset with respect to the region of highest plasma density along the beam axis, with fresh reactive gas being allowed to flow into the container and consumed gas being suctioned from the container and surfaces to be treated identically are disposed equidistantly with respect to the beam axis for the deposition of material on a deposition surface with a material generation rate of at least 400 nm/min and at a temperature of maximally 550xc2x0 C. However, significantly lower temperatures are therein possible.
From EP 0 724 026 by the same applicant as of the present invention, a method is known for the reactive treatment of workpieces in which a plasma beam is generated in an evacuated container, and radially offset with respect to the region of highest plasma density along the beam axis, are disposed workpieces, wherein fresh reactive gas being allowed to flow into the container and consumed gas is suctioned from the container, and in which, further, workpiece surfaces to be treated identically are disposed distributively about the plasma beam along a longitudinally extended surface of revolution, and specifically such that the plasma density on the surfaces is at most 20% of the maximum beam plasma density, viewed in each instance in planes perpendicular to the beam axis, which is suitable for depositing difficult to produce metastable layers, in particular of diamond, CBN, xcex1-Al2O3 or C3N4 layers. In this document it was found that the diffusion region of high-current arc discharges, i.e. the region of a plasma density of xe2x89xa620% of the beam center plasma density, is extraordinarily well suited for the deposition of extremely hard layers, in particular for the deposition of layers out of metastable phases, such as the above, difficult of generation under normal conditions.
It was found according to the present invention that this advance is not only suitable for the deposition of layers difficult to produce, but, surprisingly for the deposition fundamentally at very high deposition rates and, as stated, while maintaining low temperatures.
The use according to the invention is especially suitable for the deposition of microcrystalline silicon, therein especially highly suitable of xcexcc-Si:H.
In particular in this use it was found that with the content of hydrogen in the process atmosphere the temperatures of the treated workpieces can be set in a wide range, thus between temperatures above 400xc2x0 C. down to temperatures above 250xc2x0 C. The lower the hydrogen fraction, the lower is said temperature. Since this H2 content in the formation of xcexcc-Si:H is not particularly critical, this parameter is highly suitable as a temperature setting variable in particular when depositing this material to be used.
It should be emphasized that based on the prior known methods for very hard layers and in particular for said metastable phases which are difficult to produce, it is by no means evident that this method is suitable for the high-rate deposition, on the contrary.
The plasma beam in highly preferred manner and as described in EP 0 724 026, is developed as a low-voltage arc discharge, preferably as a high-current arc discharge.
In the use according to the invention, the deposition is used as a coating deposition or as deposition of the material in powder or cluster form, i.e. in the last cited case, to obtain said material powder or cluster. In order to carry out, furthermore, said deposition at a maximum degree of efficiency, i.e. utilized deposited quantities of material for each reactive gas quantity introduced, it is further proposed that the deposition surface is disposed along surfaces of revolution about the beam axis.
To attain maximally high efficiency with respect to the deposited quantities of material and introduced reactive gas, it is further proposed to dispose the deposition surface, be that developed by a collector surface for the deposited powder or cluster, be that formed by workpiece surfaces to be coated, annularly about the axis of the plasma beam.
In particular, if, as in the application of the use according to the invention for surface coating, the deposition thickness homogeneity is an essential criterium, it is further proposed to rotate the deposition surface about the beam axis and/or about an axis of rotation offset from the beam axis, preferably parallel hereto, during the deposition.
Homogenization of the deposition distribution is also attained through a reactive gas flow in the container generated substantially parallel to the beam axis.
In a further, highly preferred embodiment of the use according to the invention, the plasma density distribution is controlled by means of a magnetic field generated substantially parallel to the beam axis. If such a field is applied, then preferably of maximally 250 Gauss, preferably of 100 Gauss, in particular preferred of 60 Gauss.
Depending on the application purpose, the deposition surface can be placed at floating potential or at a preferably settable electric potential, therein to a DC, an AC or an AC+DC potential.
The plasma beam is further in a preferred embodiment generated by means of a low-voltage arc discharge with hot cathode or with cold cathode, preferably as a high-current arc discharge. Especially preferred and essential for the development in particular of the low-voltage/high-current arc discharge the total pressure in the container is maintaining at minimally 1 mbar.
The use according to the invention in the highly preferred embodiment is aiming for the deposition of microcrystalline silicon, in particular of xcexcc-Si:H, wherein preferably silane is employed as the reactive gas. It is therein in particular also essential that according to the invention microcrystalline silicon can be deposited in nm up to xcexcm powder or cluster form. With said high deposition rate, furthermore, as layer or powder, further silicon compounds can be deposited, such as SiC, SiN, but additionally also metal compound layers, such as in particular hard substance layer materials, such as for example TiN, TiAlN, SiAlON layers or layers with low coefficients of friction, such as CrC-, FeC-, WCC layers etc. In spite of the high deposition rates, in the deposition as coating a high coating quality suitable for epitaxial layer formation is obtained.
Furthermore, with the use according to the invention industrially widespread silicon or glass substrates are preferably coated.